The present invention relates to the structure of an image reading device employed, for example, for a multi unction device (MFD).
Copying machines and multi function devices are typically provided with an image reading device for reading images on the original to get image data. The image reading device has an image sensor such as a charge coupled device (CCD) or a contact image sensor (CIS). And images on the original are read as image data by such an image sensor scanning the original.
FIG. 1 is a cross-sectional view of the main part of a conventional image reading device, and schematically shows the structure of the image reading device. As shown in FIG. 1, the image reading device 1 has a box-shaped body frame 2. A contact glass plate 3 is provided on the top surface of the body frame 2, and the contact glass plate 3 constitutes the original table where the original is placed. Inside the body frame 2, a contact image sensor 4 is disposed. The contact image sensor 4 is disposed inside the body frame 2 so that the top surface 5 thereof faces upward. That is, the contact image sensor 4 is disposed immediately below the contact glass plate 3, and the top surface 5 of the contact image sensor 4 and the rear surface of the contact glass plate 3 are opposed to each other with a constant gap. The contact image sensor 4 reads the image from the original placed on the contact glass plate 3 while being moved in a direction vertical to the plane of FIG. 1.
Contact image sensors generally have a characteristic that the depth of field is small, and it is therefore necessary that the contact image sensor 4 be situated close to the contact glass plate 3 in order to perform excellent image reading. Further, it is important that the gap between the top surface 5 of the contact image sensor 4 and the rear surface of the contact glass plate 3 be always the same. This is because if the gap changes, since the depth of field of the contact image sensor 4 is small, the image cannot be excellently read from the original. However, there are cases where the gap changes for various reasons such as an early deformation (mainly, a deformation in the direction of the arrow 6) of the contact image sensor 4 or a posture change of the contact image sensor 4 while the contact image sensor 4 is being moved. Therefore, various improvements have previously been made to suppress the deformation of the contact image sensor 4 (or example, see Japanese Laid-Open Patent Applications Nos. 2003-92661, H9-292580, H5-323230, 2000-138803 and 2004-54156).